Retaining structures such as pins are used to secure multiple members together so that a combined pinned assembly may be created. Sometimes the combined assembly is to be permanently held together and sometimes it is desirable to disassemble the assembly so that it can be serviced, rebuilt or otherwise repaired. Based upon the design circumstances, it may be difficult to repair certain pinned assemblies due to environmental or physical constraints.
Pins may be constructed of various materials, including but not limited to metal, polymers, rubber and wood. Such pins have been utilized in numerous products and machinery throughout industry and society. Many of the materials that have been utilized to make pins and other retaining structures have been designed to perform under certain predetermined environmental constraints. However, certain environmental conditions are so severe that traditional constructs of pins structures simply cannot operate under such extreme conditions.
A pin typically has a longitudinal axis and a radii that defines a part of the geometry of the pin. The geometry of the pin traditionally has a solid construct which lends itself for use in high shear conditions. Based upon the material used, the pin will have varying compression, shear, tension and elastic characteristics. Irrespective of the material used, virtually all materials undergo a transverse contraction when stretched in one direction and a transverse expansion when compressed. The magnitude of this transverse deformation is governed by a material property known as Poisson's ratio. Poisson's ratio is defined as the transverse strain divided by the axial strain in the direction of stretching force. Since ordinary materials contract laterally when stretched and expand laterally when compressed, Poisson's ratio for such materials is positive. Poisson's ratios, denoted by a Greek nu, n, for various materials are approximately 0.5 for rubbers and for soft biological tissues, 0.45 for lead, 0.33 for aluminum, 0.27 for common steels, 0.1 to 0.4 for cellular solids such as typical polymer foams, and nearly zero for cork.
Negative Poisson's ratios are theoretically permissible but have not been successfully observed in real materials. Specifically, in an isotropic material (a material which does not have a preferred orientation) the allowable range of Poisson's ratio is from −1.0 to +0.5, based on thermodynamic considerations of strain energy in the theory of elasticity (1). It would be helpful to provide a pin structure that exhibits negative Poisson's ratio.
Repairing an assembly that utilizes a pin traditionally requires the pin to be driven out of the aperture in which it resides. This can be accomplished by using a driver to force the pin out to the aperture. However, in some circumstances a manufacturer may not want a consumer to repair such assemblies as doing so may invalidate the warranty, or even impact the integrity of the system in which the pinned assembly is being used. For example, if a manufacturer makes a part and that part should only be serviced by an approved repair technician, then it is difficult to monitor circumstances when the consumer may have attempted to repair the pinned assembly themselves. In some instances the consumer may damage a product by taking the repair into their own hands. As such, it would be helpful to provide a locking pin that has features in place that make it difficult for consumers to repair or take apart a manufactured structure, such as a pinned assembly.
It would also be helpful to provide an improved pin like structure that is made of a process where void configurations are generated in the material directly in a stress free state, whereby the pin like structure can then undergo a loaded condition resulting in a negative Poisson's ratio behavior. Such process could be used to insert a pin structure into a part, but later allow the part to be serviced again by re-loading the pin structure so as to permit the pin to be removed from the part without damaging the part.